Combine tomatoes, onions, and celery in food processor and blend until coarsely chopped. Pour into large saucepan, add chicken stock, and bring to a boil over medium heat. Simmer, uncovered, for 20 minutes. Add cream. Season with basil, salt, and pepper. Cook over very low heat for five minutes. Add cheese and cook, stirring constantly, until cheese melts. Serve at once.